1. Field of the Invention
The present invention relates generally to a design system, and more particularly, to a liquid crystal display pixel circuit designing system and a method for designing a display.
2. Description of Related Art
A spatial color filter liquid crystal display (SCF-LCD) uses white backlight module such as cold cathode fluorescent lamp (CCFL) to provide a continuous wave light source with various wavelengths and enable the continuous wave light source to pass through pixels. In general, a pixel is composed of three sub-pixels, and a field effect transistor (FET) controls the electric field intensity of each sub-pixel, so as to determine the light intensity passing through the sub-pixel. The continuous wave light source, after passing through the sub-pixels, passes through and modulated by original light (red, green or blue) filters corresponding to the sub-pixels, to obtain original light needed by each of the sub-pixels. After entering human's eyes, the original light of the sub-pixels will be blended by a human visual imaging function into a color that the pixel desires to be seen.
A field-sequential liquid crystal display (FS-LCD) modifies the light source configuration of the backlight module directly. The FS-LCD replaces the white backlight module used in the SCF-LCD with three original light sources. Therefore, the FS-LCD no longer needs the color light filters, and no need to divide each pixel into sub-pixels. In operation, the color formation of the FS-LCD is performed by modulating light emitting clocks of three original light sources in the backlight module, and coordinating FETs of the pixels to control the electric field intensity of the pixels in accordance with the corresponding clocks, to determine the light intensity passing the pixels. In short, the FS-LCD determines the intensity of light passing the pixel by modulating the light-emitting clocks of the three original light sources of the backlight module and coordinating the FETs of the pixels to control the electric field intensity of the pixels in accordance with the corresponding clocks, so as to adjust the relative intensity of the three original light with the synchronously controlled liquid crystal pixel transmission. After the three original light enter human's eyes, the human's visual system performs an integration operation on light stimulus to mix the original light into a color that the pixel is desired to be seen and form a predetermined color.
In fact, the field-sequential image-forming technique has been introduced to the market for years, and there are some modern products, such as a digital light processing (DLP) projector, has adopted this technique and proven that this technique really works and performs well. However, if this technique is applied to an LCD, there are still some bottlenecks different from the DLP projector needs to be overcome.
In display technology field, a frame has to be displayed at a frequency higher than 60 Hz, to meet the lowest changing frequency required by the human visual system to successfully integrate a complete image. Because an SCF-LCD uses a white backlight module and three original color subpixel light filters for modulation, the SCF-LCD can provide three original color light sources at the same time, and operates at an operation frequency under the requirement of the lowest changing frequency (60 Hz). However, because an FS-LCD uses three original color backlight time-changing modules to replace a continuous wave light source, the transform frequency for the three original colors has to be three times as large as that of the continuous wave light source. In other words, the FS-LCD has to have the lowest changing frequency equal to 60 Hz multiplied by 3, i.e. 180 Hz, in order to meet the lowest changing frequency required by the human visual system to successfully integrate a complete image.
If the system synchronization of the FS-LCD is poor, the response frequency of the system will not meet the requirement of the lowest changing frequency of 180 Hz, thus resulting in a color breadup (CBU) effect, and affecting user's visual effects. From the above, it is obvious that how to increase the changing frequency so as to meet the requirement of the lowest changing frequency is becoming one of the most challenging issues on applying the field-sequential image-forming technique to an LCD.
To increase the changing frequency of an LCD system, not only the changing frequency of the backlight has to meet the requirement of the lowest changing frequency, the response of a display pixel circuit also has to meet the requirement of the lowest changing frequency. Tsukada proposed a theory to analyze LCD subpixel in “TFT/LCD Liquid-Crystal Displays Addressed by Thin-Film Transistors” 2nd ed., Taylor & Francis, 2000, which the charging behavior of the pixel capacitance in a-Si TFT, dc voltage offset due to parasitic capacitance, and delay and distortion of the gate pulse. Y. H. Tai in 2006 proposed the concept of operation window based on charging, holding, coupling and delay (“Design and Operation of TFT-LCD Panels” WuNan, 2006).
In addition to meeting the requirement of the lowest changing frequency, considering the light transmission ratio of a pixel circuit is another important design concept in designing an LCD pixel circuit. In the operation of an LCD, the radiation light source passing through a pixel circuit is controlled by a voltage of the pixel circuit, if the pixel circuit has a large light transmission area, the pixel can attain high light transmission and have a better display effect, so as to reach a specific color and luminance standard with low power consumption and low cost. Y. Kaneko, A. Sasano, and T. Tsukada proposed an equivalent circuit used in designing a subpixel of an LCD (referring to “Analysis and design of a-Si TFT/LCD panels with a pixel model,” IEEE Trans. Electron Dev., vol. 36, no. 12, pp. 2953-2958, December 1989), which is a newly developed pixel model based on which a variety of LCD design models are developed. Please refer to FIG. 1. According to the equivalent circuit, persons skilled in the art not only know a basic structure of a pixel circuit, but also learn that the pixel circuit has a large portion of area which allows no light to transmit.
In designing products, design requirements and design constraints have to be considered at the same time. For example, considering the design requirements and design constraints, such as charging/discharging behaviors, potential holding, capacitor coupling effect and signal delay, comprehensively, is one of the most important issues in designing a pixel circuit. However, no designing system has ever been proposed to consider the above design parameters of the display pixel circuit at the same time and to operate, compare and display effect variations of a variety of designs corresponding to design parameters and help a designer to select ideal design parameters for aiding in designing a display pixel circuit.
Therefore, how to provide a display designing system, which operates, compares and displays effect variations of a variety of designs corresponding to design parameters and helps a designer to select ideal design parameters for aiding in designing a display pixel circuit, is becoming one of the most urgent errands in the art.